1. Field of the Invention
The present invention relates generally to measuring a process kit part, and more particularly to a system for monitoring the accumulation of deposits and wear on plasma process kit parts.
2. Discussion of the Background
The semiconductor industry employs plasma processing tools to etch and deposit materials on the substrates for integrated circuit (IC) devices. Plasma can be formed in numerous sources, including a capacitively coupled plasma (CCP) source, an inductively coupled plasma (ICP) source, an electrostatic radio frequency (ESRF) source, or any combination thereof.
Regardless of the source, plasma is typically formed by ionizing a process gas with high energy electrons, in a plasma chamber housing an IC substrate. Depending upon the conditions (e.g., temperature and pressure) and choice of process gas, reactive plasma is formed that suits the particular process being performed in the chamber. In an etching process, material is removed from the substrate surface, while a depositing process will deposit material on the substrate surface.
Unfortunately, plasma processing also removes and deposits material on the plasma process kit parts inside the plasma chamber. Once too much material accumulates on a process kit part, it may flake off and circulate within the chamber, eventually contaminating substrate surfaces and vital chamber components. Further, parts subjected to chamber processing or part cleaning techniques may become eroded or worn. Because process kit parts must remain within exacting size tolerances, excessive deposits and wear can impact process performance within the chamber.
To guard against such problems, process kit parts must be cleaned or replaced. However, cleaning causes additional wear and replacement can be costly. Further, both result in down-time for personnel and equipment. In order to minimize wafer production costs, cleaning or replacement of a process kit part should be done only when the part is unable to function properly in the process chamber. Thus, process kit part dimensions are frequently measured, not only to ensure compliance with strict tolerances, but to avoid premature cleaning and replacement.
Conventionally, measurement metrology techniques, such as measuring the part with precision calipers or some other general purpose measuring tool, are utilized. However, such techniques typically require disconnecting and removing process kit parts from their plasma chambers, which can be labor intensive, and often results in down-time for personnel and plasma processing tools. Moreover, use of general purpose measuring tools to test a process kit part requires accurate reading of the tool as well as knowledge of the desired dimension for the particular process kit part being measured. These requirements can lead to false indications of the status of a part.
An alternative method of determining the status of a part is by manufacturing the process kit part with a mark such as an etch or scribe mark, the visibility of which aids in determining whether a process kit part is within tolerance. For example, a mark may be formed by scribing a symbol to a particular scribe depth in the part. When the part is subject to processing and cleaning, one can determine whether the part has eroded beyond the scribe depth by simply verifying whether the symbol is visible or not. However, this method requires a specially manufactured part and is not useful for determining material accumulation on a part. Moreover, as process kit parts may have different tolerances for different processes performed in the chamber, the scribe depth must be specific to the chamber process that the part will be exposed to. This may result in an otherwise generic process part becoming process specific.